17.4. Extension Point

An extension point describes a point in a use case where
an extending use case may provide additional behavior.

Examples for a travel agent sales system might be the use
case for paying for a ticket, which has an extension point in
the specification of the payment. Extending use cases may then
extend at this point to pay by cash, credit card etc.

Within the UML metamodel, Extension
Point is a sub-class of
ModelElement. A use case may display an extension
point compartment (see Section 17.3, “Use Case” for
details), in which extension points are shown with the
following syntax.